1. Field of the Invention
The present invention relates in general to liquid crystal display devices and, in particular, to a liquid crystal display device including a liquid crystal display panel of an IPS system having a comb-like electrode and a planar electrode disposed to sandwich an insulating film therebetween.
2. Description of the Related Art
Significant advances have lately been made in display performance of liquid crystal display devices including a liquid crystal display panel as a display device and such display devices have met many application fields. Use of the liquid crystal display panel, in particular, permits a thinner and lighter display device main unit that consumes less electric power. The liquid crystal display panel is thus used as display devices of varying sizes from large-sized ones, such as TV receivers and monitors of information processing units, to small-sized ones, such as portable information terminals.
The liquid crystal display panel, for its outstandingly excellent characteristic as compared with conventional display devices, is widely used even in, for example, medical diagnostic imaging units. In a typical medical diagnostic imaging unit, a doctor as an interpreter of a radiograph makes a diagnosis based on a diagnostic image having a wide dynamic range imaged by, for example, X-ray equipment or tomographic X-ray equipment and displayed on a display device. The display device used for medical X-ray diagnostic equipment is therefore required to offer an extremely high display luminance and image display performance in a wide dynamic range for providing high gradation performance required for interpreting the diagnostic image.
A liquid crystal display device is disclosed, for example, in JP-A-2008-521049 as a technique for satisfying these requirements. The liquid crystal display device disclosed in JP-A-2008-521049 includes two liquid crystal display panels imposed one on top of another, wherein an image with lower resolution is displayed on a liquid crystal display panel closer to a backlight as a light source than a liquid crystal display panel remote therefrom, to thereby make the liquid crystal display device capable of displaying an image with a wide dynamic range.
JP-A-2009-122595 discloses a technique for forming, in a liquid crystal display device of an IPS system, a planar first electrode for each of pixels disposed in a matrix pattern and a second electrode (a linear electrode, a comb-like electrode) formed of a comb-like electrode and a slit via an insulating film. Through the foregoing arrangement, the technique disclosed in JP-A-2009-122595 reduces an unusual domain at a slit end, specifically, region in which a liquid crystal is not controlled by an image signal applied to the pixel, thereby improving transmissivity of the liquid crystal display device to achieve image display with high luminance.